1. Field of the Invention
The present invention relates to the structure of a stator for an electric motor, and more particularly to a structure for providing an electrical insulation between the stator core and windings forming coils. The present invention also relates to a method for fabricating the stator core of an electric motor, and more particularly to a stator core fabricating method preferable to achieve a reliable electrical insulation to the coil.
2. Description of the Related Art
Motors commonly include stators, each including a stator core and coils formed by winding plural pieces of wire (conductors). The stator core is usually formed by laminating annular magnetic steel plates each which has its inner side formed in a comb-like pattern. The teeth arranged in a comb-like pattern act as a magnetic pole. A coil is formed by winding wire conductors around a tooth though each slot or groove. The magnetic steel plate is formed through an accurate punching process. This process tends to produce burrs around the edge of the magnetic steel plate. Conductors coated with insulation layers tend to be damaged by the burrs of the magnetic steel plate. Conventionally, in order to prevent damages of the insulating layers, an insulation paper is inserted between the inner surface in the slot and the conductor. Japanese Laid-open Utility Model publication No. Sho 58-183054 discloses the technique of forming an insulating layer on the slot surfaces of a stator core to secure good electrical insulation.
The edge around the fringe of the magnetic steel plate is sharp and may include burrs as described above. Particularly, since conductors, when being wound around the stator, are strongly in contact with the edge of the slot at the end of a stator, the insulation layer thereon is prone to be easily damaged. It has been difficult to form an insulating layer thick equal to that on the flat portion on the edge of the stator core, even by using the technique disclosed in the above-mentioned publication, so that the insulation layers coated on the conductor is possibly damaged at the edge of the slot or the corner. Hence, a reliable electrical insulation cannot be sufficiently secured at the critical portion.